1. Field of the Invention
This invention relates generally to a method and apparatus for selectively feeding sheets of paper from a plurality of stacks of paper to a printer and, more particularly, a single apparatus for selectively engaging multiple stacks of paper and feeding single sheets from the selected stack of paper to a printer.
2. Description of the Related Art
In the field of printers and, in particular, electrophotographic printers, such as desktop laser printers, paper handling mechanisms typically employ a separate sheet feeding mechanism for each tray of paper that the laser printer has the ability to access. These trays typically are configured to hold approximately 250 sheets of paper and include a bottom portion that supports the stack of paper and is hinged to allow the stack of paper to be pivoted upward and against the stationary sheet feeding mechanism associated with that tray. Pressure is maintained between the sheet feeding mechanism and the stacks of paper by a spring acting against the hinged bottom portion.
Therefore, when the laser printer includes a paper handling mechanism that has more than one tray, each tray ordinarily has a dedicated sheet feeding mechanism associated therewith. These pairs of trays and sheet feeding mechanisms are normally stacked in a vertical arrangement and consume vertical space equal to the height of the 250 sheet tray and the vertical height of each sheet feeding mechanism. Accordingly, the vertical height of each tray and sheet feeding mechanism limits the maximum number of trays that can be associated with a paper handling mechanism of a laser printer. Combining more than a preselected number of trays and sheet feeding mechanisms simply produces a paper handling mechanism that is too large for a desktop environment.
Further, it should also be appreciated that the pressure between the sheet feeding mechanism and the stack of paper varies with the thickness of the stack of paper remaining in the tray. That is to say, the force applied by a spring is nonlinear since it is dependent upon the degree of compression of the spring. As the height of the stack of paper changes, the compression of the spring necessarily varies therewith, and the force applied by the nonlinear spring must also similarly vary.
Moreover, since the sheet feeding mechanism is stationary and the spring force applied to the stack of paper in its associated tray is accomplished by a spring located in the paper handling mechanism, the paper is constantly maintained in contact with the sheet feeding mechanism. Thus, when additional paper is loaded into a particular tray, the printing process from that tray must cease while the tray is removed and the paper supply replenished. This is particularly important where the user wishes to print a short run of unique paper that differs from the paper currently located in the tray.
To overcome this inherent deficiency, previous laser printers have employed a single sheet feeding mechanism whereby an operator desiring to print a small number of copies on a paper style unique from that currently loaded in the trays may singularly and consecutively feed the number of sheets required for the printing process. This, of course, is a time intensive process that does not free the user to accomplish other tasks, but requires that the user remain at the printer, consecutively feeding each sheet of paper until the entire printing process is completed.
Alternatively, the user may remove the tray from the paper handling mechanism, insert the desired number of sheets of paper into the tray and replace the tray into the paper handling mechanism. While this method does free the user to leave the area of the printer during the printing process, the procedure of removing the tray and loading the tray with a precise, preselected number of unique sheets of paper is also a laborious and time intensive task.
Additionally, the market for desktop laser printers is highly competitive and, therefore, extremely cost sensitive. Accordingly, it is desirable that any proposed solution to these above-identified problems be economical, durable, and simple in design, construction, and repair.
The present invention is directed to overcoming one or more of the problems as set forth above.